function sendAjaxReq()

 {

     //1,创建ajax引擎 XMLHttpRequest对象

     var req = new XMLHttpRequest() || new ActiveXObject("Msxm12.XMLHTTP");

     //2,打开一个请求，此时未发送请求，定义好发送请求的方式以及是否需要携带数据 是否同步异步

     req.open("get", "testAjax?phone=iphone&apple=pen");

     //3,准备好处理服务器返回的数据

     req.onreadystatechange = function()

     {

         if(req.readyState == 4)

         {

             //返回json数据的解析格式

             var str = req.responseText;

             eval("var obj=" + str);

             alert(obj.name);

             //返回xml的解析格式

             var data = req.reponseXML.getElementsByTagName("bigName")[0].first(child.data);

         }

     }

     //4,发送请求,如果是在火狐下，使用get方式发送ajax请求，send的时候括号写上null

     req.send(null);

 }

 //使用post传参，需要携带一个请求头模拟表单提交

 function sendAjax()

 {

     var request = new XMLHttpRequest() || new ActiveXObject("Msxm12.XMLHTTP");

     request.open("post", "testAjax?phone=1", true)

     request.onreadystatechange = function()

     {

         if(request.readyState == 4)

         {

             if(request.status == 200)

             {

                 var str = request.responseText;

                 alert(str);

             }

             else if(request.status == 404)

             {

                 alert("找不到资源");

             }

         }

     }

     request.setRequestHeader("content-type", "application/x-www-form-urlencoded")

     request.send("phone=");

 }

 function sendAjaxReq(method,url,param,fun200,fun404,fun500)

  {

      var req;

       if(window.XMLHttpRequest)

       {

           req = new XMLHttpRequest();

       }

           else if(window.ActiveXObject)

       {

          req = new ActiveXObject("Msxml2.XMLHTTP");

       }

       req.open(method,url);

       req.onreadystatechange = function()

       {

           if(req.readyState == 4)

           {

               if(req.status == 200)

               {

                   if(fun200)

                   {

                      fun200(req.responseText);

                   }

               }

               else if(req.status == 404)

               {

                   if(fun404)

                   {

                       fun404();

                   }

               }

               else if(req.status == 500)

               {

                   if(fun500)

                   {

                       fun500();

                   }

               }

           }

       }

       if(method.toUpperCase() == "GET")

       {

           req.send(null);

       }

       else if(method.toUpperCase() == "POST")

       {

           req.setRequestHeader("context-type", "application/x-www-form-urlencoded");

           req.send(param);

       }

   }

 function testAjax()

 {

     sendAjaxReq("get","ajaxServlet?uname=1&password=2",null,function(data)

     {

         eval("var obj="+data);

         alert(obj.data);

     });

 }